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Scientists synthesize a molecular "cage" to trap chloride



  Building a better salt trap: Scientists synthesize a molecular
computer rendering of the cage with six triazole molecules to trap chloride salts. Photo credits: Yan Liu, University of Illinois, Urbana-Champaign

Indiana University researchers have developed a powerful new molecule for the extraction of salt from liquids. The work can help to increase the amount of drinking water on earth.

The new molecule was made using chemical bonds previously considered too weak, and is about ten billion times better than a similar structure made at IU over 1

0 years ago. The design of molecules was reported on May 23 in the journal Science .

"If you put one millionth of a gram of this molecule into a ton of water, 100 percent of it will remain able to capture a salt," said Yun Liu, who led the study as a graduate student. Student in the lab of Amar Flood, Professor of Chemistry with James F. Jackson and Professor of Chemistry with Luther Dana Waterman at the Department of Chemistry of the Bloomington College of Arts and Sciences of the IU.

The molecule is said to capture chloride that is formed when the element chlorine mates with another element to obtain an electron. The best known chloride salt is sodium chloride or ordinary table salt. Other chloride salts are potassium chloride, calcium chloride and ammonium chloride.

As the human population continues to grow, the penetration of salt into freshwater systems reduces access to drinking water around the world. In the US alone, the US Geological Survey estimates that 271 tonnes of dissolved solids, including salts, enter freshwater streams each year. Factors include the chemical processes involved in oil extraction, the use of ground salts and water softeners, and the natural weathering of rocks. With only a teaspoon of salt, five gallons of water are permanently contaminated.

The newly developed salt extraction molecule at the IU consists of six triazole "motifs" – five-membered rings of nitrogen, carbon and hydrogen forming a three-dimensional "cage" that is perfectly shaped to trap chloride. In 2008, Flood's lab created a two-dimensional flat donut molecule using four triazoles. The two additional triazoles give the new molecule its three-dimensional shape and increase its activity by ten billion times.

The molecule is also unique in that it binds chloride through carbon-hydrogen bonds that were previously considered too weak to produce stable interactions with chloride compared to the traditional use of nitrogen-hydrogen bonds. Despite all expectations, the researchers discovered that the use of triazoles creates a cage that is so rigid that it creates a vacuum in the center that absorbs chloride ions.

<img src = "https://3c1703fe8d.site.internapcdn.net/newman/csz/news/800/2019/3-buildingabet.jpg" alt = "Making a Better Salt Trap: Scientists Synthesize a Molecular" Cage [To capture chloride] [19659011] Yun Liu has a 3D-printed model of the six-triazole molecule for capturing chloride salts Image credits: Fred Zwicky, University of Illinois, Urbana Champaign.

In contrast, cages with nitrogen-hydrogen bonds are often more flexible – and the vacuum-type center required for chloride deposition requires energy input, which lowers their efficiency compared to a triazole-based cage.

Take our molecule and stack it against other cages that use [stronger] bonds. We're talking about increasing the performance in many orders of magnitude, "said Flood." This study really shows that rigidity is underestimated in the construction of molecular cages. "

The rigidity also allows the molecule to retain its shape after the central Chloride has been lost compared to other constructions that collapse under the same circumstances due to its flexibility .This increases the efficacy and versatility of the molecule.

The work is also reproducible.The synthesis of the first molecule took almost a year, said Liu: He was shocked to discover the crystals needed to confirm the unique structure of the molecule that had formed after the experiment had been left in the lab for several months.

The formation of the crystal was noted a "eureka" moment and proved that the unique design of the molecule actually I was realizable. Later, Wei Zhao, a postdoctoral researcher in Flood's lab, was able to rebuild the molecule in several months.


Keep the taste, reduce the salt


Further information:
"Chloride Deposition with a CH-Hydrogen Bond Cage" Science (2019). science.sciencemag.org/cgi/doi… 1126 / science.aaw5145

Provided by
University of Indiana




Quote :
Building a Better Salt Trap: Scientists Synthesize a Molecular "Cage" to Capture Chloride (2019, May 23)
retrieved on May 23, 2019
from https://phys.org/news/2019-05-salt-scientists-molecular-cage-chloride.html

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